= late symptoms of DNA retrovirus infection attacking monocytes + macrophages → deficient cell-mediated immunity

Incidence: 1,200,000 HIV-seropositive persons (0.3% of population) in USA IN 2011; 14% undiagnosed; 50,000 new HIV infections per year

Histo: formation of microglial nodules instead of granulomas in 75–80% of autopsied brains

• neurologic symptoms as initial complaint in 7–10%, ultimately afflict up to 40–60%: personality + mental status changes, headache, memory loss, difficulty to concentrate, depression, confusion, dementia, new onset of seizures, focal deficit from mass lesion
• Any male with neurologic symptoms between age 20 and 50 has AIDS until proven otherwise
• Unusual presentations are clues to HIV infection: pansinusitis, mastoiditis, parotid cysts, cervical adenopathy, hypointense spine

Rx: azidothymidine (AZT)

1. ATROPHY:
   1. Malnutrition, dehydration, steroid therapy, chronic dialysis, normal aging
   2. AIDS dementia complex (ADC)
      = SUBACUTE ENCEPHALITIS = HIV encephalitis
      = cognitive disturbances → progressing to dementia
      Etiology: HIV-1 infection of CNS macrophages generating neurotoxic factors
      Prevalence: 7–27% of AIDS patients
      Histo: predominantly perivascular HIV encephalitis; HIV leukoencephalopathy characterized by diffuse myelin loss + infiltration by macrophages
      • cerebral atrophy
      • subtly increased signal intensities on T2 and FLAIR sequences without mass effect ← leaky capillaries with egress of water:
        • focal / diffuse
        • symmetric / asymmetric
        • reversible / nonreversible
   3. INTRAAXIAL LESION WITHOUT MASS EFFECT
      1. Progressive multifocal leukoencephalopathy
   4. MASS LESION
      1. Toxoplasmosis
      2. Primary CNS lymphoma (PCNSL)
      3. Fungal, granulomatous, viral, bacterial infection
         1. Cryptococcosis
         2. Other opportunistic CNS infections:
            • tuberculosis
            • neurosyphilis
   • With multiple CNS lesions toxoplasmic encephalitis is the more likely diagnosis!
   • With a single CNS lesion the probability of lymphoma is at least equal to toxoplasmosis!